CZ 286113 (EP1051595B1) discloses a method for detecting the thickness and/or homogeneity of moving yarn, in which the yarn moves in a radiation flux between a radiation source and a linear CCD detector, whereby each of the elements of the CCD detector is coupled with an evaluation device of the state and/or degree of its irradiation. CCD detectors are used as sensors of radiation, monitoring the yarn to be measured discontinuously always on very short sections of approximately 10 μm in length.
The patent U.S. Pat. No. 6,242,755 B1 describes a method for the contactless measuring of fibrous textile material of indeterminate length, in which the textile material is placed within a radiation range of at least one source of radiation and its shadow is projected by the radiation onto a receiving device comprising a row of sensor cells arranged next to one another, whereby the receiving device is composed of a CCD detector. The diameter of the fibrous textile material is determined on the basis of the number of fully shadowed sensor cells and from partial shadowing of one or two neighbouring sensor cells, the value of the partial shadowing being determined proportionally according to the amount of the partial shadowing to the amount of the fully covered sensor cells.
To date, known yarn cleaners based on linear CCD detectors or CMOS optical detectors and intended for installation on spinning or weft-winding machines, work only with digital values of the number of shadowed optical elements. Even though the patents CZ 286 113 and U.S. Pat. No. 6,242,755 disclose methods of evaluation of the yarn diameter including the influence of partially irradiated optical elements, such detectors have not been realized yet in industrial applications, very probably due to the difficulties and disadvantages that have been overcome by the present invention. Apparently, the processing of analog signals from the individual optical elements of the detectors, if not accompanied by other measures, such as those preventing electromagnetic disturbances, is complicated and does not lead to the desired effect.
U.S. Pat. No. 6,219,135 (EP 1015873 B1) describes a configuration of an optical detector, combining analog and digital optical elements with the purpose of obtaining not only the information about the yarn diameter, but also the information about the surface structure of the yarn. Supposedly, this device is intended for use only as part of laboratory apparatuses. However, if the device is to be used as a measuring device online during the production of yarn, it has a number of shortcomings. A major disadvantage is the fact that it is impossible to set the sensitivity of analog optical elements in dependence on the changing conditions of the environment, such as ambient light and the contamination of the detector and/or the radiation source with dust and other impurities. Another disadvantage is that the alternating-current component of a signal from the analog optical elements defining the surface structure of yarn is modulated at a relatively great direct-current component, which worsens the processing of the signals by the analog-to-digital converter. Another drawback is the fact that the analog signal is carried to be processed outside the detector itself, being exposed to the influences of electromagnetic disturbances which are induced into the analog conductor from the other devices of the machine operating in the vicinity of the detector. Apparently, disturbance-free environment can be realized when using the optical detector in a laboratory, but it can be achieved with difficulty if the device is used directly on production machines.
The disadvantages during the processing of an analog signal were eliminated by a device for the contactless measuring of moving yarn according to the patent CZ 299684, in which a linear optical detector is incorporated into one semiconductor application specific integrated circuit (ASIC) along with at least a part of electronic circuits for the processing and/or evaluation of a signal of the linear optical detector, whereby the electronic circuits for the processing and/or evaluation of a signal of the linear optical detector are integrated along with the linear optical detector on a common semiconductor support and/or mounted in one common case.
The advantage of this arrangement is especially the fact that the initial operations of the processing and/or evaluation of a signal of the detector take place in one integrated circuit, and so the output signal is not influenced by disturbances, nevertheless the solution according to CZ 299 684 is based only on the binary processing of the signals from the individual optical elements when only the irradiation or shadowing of each individual optical element is monitored. The disadvantage of this solution is a purely digital evaluation of the individual optical elements, when, according to a set comparison level, the individual optical elements are divided into irradiated and non-irradiated, the information about the yarn diameter is represented by the sum of the widths of the shadowed optical elements. This device, therefore, does not permit a sufficiently precise evaluation of the surface structure of yarn and, what is more, it is rather difficult to monitor possible contamination of the individual optical elements with dust or other impurities or to monitor changes in the intensity of the light source.